import java.util.Vector;

public class HashTable {

    private Vector<Pair> table;
    int size;
    final static Pair Empty = new Pair(null,null);
    final static Pair Deleted = new Pair(null,null);

    public HashTable(int s) {
	size = s;
	table = new Vector<Pair>(s);
	for(int i=0;i<size;i++)
	    table.add(i,Empty);
    }
   
    //*** This bad hash function is for illustration only.
    //*** Do not use it.

    private int hash(String key, int s) {
	return (key.charAt(0)*26 + key.charAt(1)) % s;
    }

    public Pair find(String key) {
	for(int n=hash(key,size); 
	    table.get(n)!=Empty; 
	    n=(n+1)%size)
	    if(table.get(n)!=Deleted 
	       && table.get(n).getFirst().equals(key))
		return table.get(n);
	return null;
    }

    public void modify(String key, Object data) {
	Pair p = find(key);
	if(p != null)
	    p.setSecond(data);
    }

    public void add(String key, Object data) {
	// Pre: k not already in the hash table.
	int n;
	for(n=hash(key,size); 
	    table.get(n)!=Empty && table.get(n)!=Deleted;
	    n=(n+1)%size) 
	    {}
	table.set(n,new Pair(key,data));
    }

    public void delete(String key) {
	for(int n=hash(key,size); 
	    table.get(n)!=Empty; 
	    n=(n+1)%size)
	    if(table.get(n)!=Deleted 
	       && table.get(n).getFirst().equals(key)) {
		table.set(n,Deleted);
		return;
	    }
    }

    public int getNumberCollisions() { return 0; }
}